1. Field of the Invention
The present invention relates generally to video camera systems and, more particularly, is directed to a video camera system suitably applied to a communication between a camera head unit and a camera control unit.
2. Description of the Prior Art
A prior-art video camera system for a studio or for a field pick-up van is constructed as shown in FIG. 1.
Referring to FIG. 1, there is shown a camera head unit (CHU) 1, i.e., a video camera body which is comprised of a solid state imager such as a charge coupled device (CCD) and the like, a head amplifier, a lens 4 of an image pick-up system and so on. Further, the camera head unit 1 includes a viewfinder 2, a microphone 3 for collecting a sound when a cameraman takes a picture, and a headset 5 composed of a headphone (not shown) and a microphone (not shown) and which is worn by the cameraman on the head or the like to communicate with the studio.
The camera head unit 1 derives a video signal 8 such as, a luminance signal Y (8a), a color difference signal U/V (8b) and the like. This video signal 8 is transmitted through a coaxial cable 7 to a camera control unit (CCU) 9 located in the studio or in the field pick-up van 10 side. The video signal 8 picked-up by the aforenoted video camera is, for example, FM-modulated and transmitted through the coaxial cable 7. The camera control unit 9 generates control and adjusting data, etc.
Within the studio or the field pick-up van 10, there are provided a control panel 11 for performing video signal processing, an audio mixing console 12 for mixing audio signals, etc. While watching a monitor receiver 17, an audio level meter (not shown) or the like, a video and audio mixer 14 adjusts the image signal and the sound signal supplied thereto from the camera head unit 1, whereby a video signal 15 and an audio signal 16 are converted, for example, to an NTSC television signal and broadcast.
In addition to the luminance signal 8a and the color difference signal 8b forming the video signal 8, data 19, a return video signal 22, a first microphone signal 20L, a second microphone signal 20R, an intercom signal 21, a power source voltage signal 18 such as an AC voltage signal of 240 V, etc., are transmitted through the coaxial cable 7 connecting the above-described camera head unit 1 and camera control unit 9, as shown in the signal allocation of FIG. 2. The return video signal 22 is a video signal transmitted to the camera head unit 1 side from the camera control unit 9 side through the coaxial cable 7 such that a video signal picked-up at the camera head unit 1 side and which is adjusted, received and reproduced by the control panel 11 while watching the monitor receiver 17 is transmitted through the camera control unit 9 and can be again reproduced at the viewfinder 2 provided at the camera head unit 1 side.
As shown in FIG. 2, the DC or AC voltage source signal 18 utilized in the circuits (not shown) at the camera head unit 1 side is transmitted as a voltage signal of, for example, AC voltage of 240 V. Left and right audio signals collected by the microphone 3 are transmitted as the first and second microphone output signals 20L and 20R. The intercom signal 21 is used to communicate the cameraman 6 who operates the camera head unit 1 with the video or audio mixer 14 in order to discuss technical problems or to make broadcast programs. The data 19 are control data which are utilized for the camera control unit 9 side to adjust white balance, automatic iris control and the like in the camera head unit 1 side. These signals or data 19 are frequency-divided and frequency-multiplexed so that they can be transmitted to two directions.
FIG. 3 is a block diagram showing a transmission system of the above-described intercom signal 21, in particular, a so-called talk side thereof.
As shown in FIG. 3, a plurality of video camera apparatus, i.e., camera head units 1 are connected through a plurality of camera control units 9 to, for example, the headset 13 of the mixer 14 at the audio mixing console 12 side, whereby the mixer 14 communicates with a plurality of cameramen 6, 6, . . . who operate the plurality of camera head units 1, 1, . . . via the intercom signal 21.
Referring to FIGS. 1 and 3, communication signals from the microphones of the headsets 5 worn by the cameramen 6 of n camera head units 1, 1, . . . are supplied to input terminals 23a to 23n. The communication signals applied to the input terminals 23a to 23n are supplied through switches 24a to 24n to amplifying circuits 25a to 25n and are thereby amplified. The communication signals amplified are, for example, FM-modulated by FM-modulators 26a to 26n and transmitted through the coaxial cables 7 to the camera control unit 9 side, in which they are demodulated by demodulators 27a to 27n to provide original communication signals. The resultant communication signals are amplified by output amplifying circuits 28a to 28n and then supplied through output terminals 29a to 29n to an adding circuit 30 provided within the audio mixing console 12 in the studio or in the field pick-up van 10 and thereby added. The added signal is amplified by an amplifier 31, and is then transmitted through an output terminal 32 to the receiver of the headset 13 that the mixer 14 wears on the head. In other words, the mixer 14 can receive the communication signals from the plurality of cameramen 6, 6, . . . at a time if the communications are performed simultaneously under the condition that the switches 24a to 24n provided at the camera head units 1 are turned ON.
According to the prior-art video camera system shown in FIG. 3, with respect to the side of the headset 13 worn by the mixer 14 who operates, for example, the audio mixing console 12 provided within the studio or field pick-up van 10, although the switches 24a, . . . , 24n provided at the camera head unit 1 side are turned OFF, a noise level limit of the coaxial cable 7, for example, an FM noise produced through the modulation and demodulation circuits and the like are added to the communication signals and then outputted. For example, if there are provided 10 camera head units 1, the noise component is added 10 times as great and is then transmitted to the headset 13 side.
The intercom signal 21 shown in FIG. 2 is composed of two systems as shown in FIG. 4: One system is formed of intercom signals 21a, 21c (hereinafter simply referred to as PRD.sub.IN, PRD.sub.OUT) which are intercommunicated between the producer at the studio 10 side and the cameraman 6 in order to make the broadcasting program, and intercom signals 21b, 21d (hereinafter simply referred to as ENG.sub.IN, ENG.sub.OUT) which are used to communicate the cameraman 6 and the engineer at the studio 10 side in order to cope with a camera trouble and the like. Nevertheless, the intercom signal network lines of two systems are not limited to the producer or to the engineer and may be freely changed by the users. For this reason, if the two systems of the intercom signals of PRD.sub.IN, PRD.sub.OUT /ENG.sub.IN, ENG.sub.OUT are switched as in the prior art, there occurs a problem of a cumbersome work for rearranging the matrix, when the intercom signals of two systems are utilized in various ways by the user.
FIG. 5 is a block circuit diagram useful for explaining a method of adjusting a level of an audio signal when an output signal such as an audio signal from the above-described microphone 3 or the like is transmitted from the camera head unit 1 side to the camera unit 9 side.
Referring to FIG. 5, the first or second microphone output signal 20L or 20R such as a left or right audio signal is collected by the microphone 3 and is then supplied to an input terminal 50. The microphone output signal 20L or 20R is supplied through a pre-amplifier 51 to a modulating circuit 52, in which it is, for example, FM-modulated. The thus FM-modulated signal is transmitted through the coaxial cable 7 to the camera control unit 9 side. Then, by a demodulating circuit 53 in the camera control unit 9 side, this transmitted signal is demodulated to provide a first or second original analog microphone output signal 20L or 20R. This first or second analog microphone output signal 20L or 20R is supplied to a variable gain amplifying circuit 54, in which it is controlled in gain, and is then fed through an output terminal 55 to the audio mixing console 12 provided within the studio 10. Thus, the gain-controlled signal microphone output signal 20L or 20R is adjusted to be a pre-determined level and is then broadcast.
Alternatively, the following audio level adjusting method has been used in the past. In this method, a audio gain adjusting device is provided at the camera head unit 1 side for manually adjusting the audio level. In that case, the mixer 14 at the camera control unit 9 side supplies from the headset 13 thereof the cameraman 6 with a gain level command via the intercom signal 21 so that the cameraman 6 determines a pre-determined level by operating the audio gain adjusting device on the basis of the command issued by the mixer 14.
According to the thus constructed prior-art video camera system, the first or second microphone output signal 20L or 20R is collected at the camera head unit 1 side with a pre-determined level, and the gain of the first or second microphone output signal 20L or 20R is adjusted by the variable gain control amplifying circuit 54 in the camera control unit 9 side. Thus, the gain-adjusted first or second microphone output signal 20L or 20R is supplied from the output terminal 55 to the audio mixing console 12 side.
When surrounding sounds and so on are collected by the microphone 3, the audio level is considerably fluctuated in response to the conditions of circumstance. In general, the level of sound when the sound is collected by the microphone 3 is approximately -60 dB (2.2 m VPP). When this audio signal or the like is transmitted through the coaxial cable 7, a pre-determined noise level determined by the coaxial cable (TRIAX) 7 exits so that, when the level of the sound collected by the microphone 3 is reduced, a signal-to-noise (S/N) ratio relative to the noise level determined by the coaxial cable 7 is deteriorated. On the other hand, a dynamic range of an audio signal that can be transmitted via the coaxial cable 7 is about 20 dB so that, even when the microphone level is increased, the transmission level is suppressed to approximately 20 dB.